Method for monitoring a braking torque modification of a retarder

ABSTRACT

The invention relates to a method for monitoring a braking torque modification of a retarder, in particular of a motor vehicle, said braking torque modification being controlled by an actuating pressure control circuit comprising a pressure sensor that is connected in said circuit. The method comprises the following steps: the actuating pressure of the retarder is dynamically detected by means of the pressure sensor that is mounted in the actuating pressure control circuit; the temporal progression of the detected actuating pressure is compared with at least one predetermined target progression; a warning is issued and/or a future activation of the retarder by a user, in particular the driver of the vehicle, is prevented, based on the actual-target comparison and if predetermined criteria have been fulfilled.

The present invention relates to the monitoring of a braking torquemodification of a retarder, whereby the braking torque modification iscontrolled by an actuating pressure control circuit. In particular theinvention relates to a method for the monitoring of a braking torquemodification or for the monitoring of a braking torque modification andfor the detection of errors.

Usually retarders of motor vehicles as well as comparable systems arecontrolled or steered by means of actuating pressure (pneumatic pressurepY) that can be metered regularly or continuously, whereby a pressuresensor is installed in the actuating pressure control circuit. Thispressure sensor is used exclusively for control purposes or fortolerance minimization in the setting of a predetermined actuatingpressure for the retarder. FIG. 1 shows such a retarder system with anelectronic control unit, whereby the retarder is labeled with referencesymbol 1, the pressure sensor with reference symbol 2, and the electriccontrol unit is represented by reference symbol 3, as well as anelectro-pneumatic valve represented by reference symbol 4. P_(v)designates the pressure of a reservoir system for the working fluid ofthe retarder, whereby the working fluid is for example stored in an airbrake reservoir.

Since retarders, also called hydrodynamic brakes, have the function ofan additional braking system, deactivation or immobilization in the caseof an error is permissible for example in the control system. Simplyput, this means that the safe state is the off state. In the developmentof retarder systems one is hence endeavoring to provide means for thesafe deactivation of the retarder as well as the securing of thisdeactivation during the entire service life of the retarder system. Anundesired modification of the deactivation behavior of a retarder canresult in damage to the vehicle system or in the worst case scenario,can lead to accidents. Thus, for example, in the case of a too slowdeactivation of the retarder in a critical situation the danger existsthat the vehicle will skid.

The invention is based on the object of presenting a method formonitoring a predetermined braking torque modification which on the onehand stands out due to a high reliability and on the other hand can beimplemented in an existing retarder overall system without considerableadditional expense or in particular without causing the provision ofadditional components.

The object of the invention is solved by a method with the features ofclaim 1, further by an inventive usage in accordance with claim 13. Thedependent claims describe particularly expedient embodiments of theinvention.

By means of the inventive method it is possible to make available asecure monitoring of a braking torque modification, for example adeactivation process or an activation process. In accordance with theinvention the pressure sensor that is present in the actuating pressurecontrol circuit of the retarder is used for detection of the dynamicprogression of the actuating pressure, whereby the control circuit isused to control the retarder braking torque by the application of apredetermined actuating pressure on the retarder input. This detecteddynamic progression hence represents an actual progression and iscompared with at least one predetermined target progression. Using theresults of this target-actual comparison, provided predeterminedcriteria are fulfilled, for example when the actual progression deviatesfrom the target progression by a predetermined extent, a warning isissued and alternately or in addition the retarder or the retardercontrol, which takes place by means of a retarder control unit, can beset to a state which prevents a future activation of the retarder by thedriver of the vehicle. In a manner of speaking the retarder isimmobilized. Such an immobilization can then be overridden again, forexample by a specialist repair shop after elimination of the defectswhich resulted in the deviation of the actual progression in comparisonwith the target progression.

In accordance with an expedient embodiment of the invention the targetprogression is predetermined in the form of at least one targetcharacteristic. Such a characteristic can for example be stored in theretarder control unit. The retarder control unit also expedientlyperforms the comparison of the actual progression with the targetprogression. In accordance with an expedient embodiment of the inventionat least two target characteristics are predetermined, namely a firstwarning characteristic and a second mobilization characteristic. Upon“violation” of the warning characteristic by the actual progression awarning is issued, while upon “violation” of the immobilizationcharacteristic the above described immobilization of the retarder isperformed. How such a “violation” of the characteristics can be detectedand assessed will be described in detail in the following.

The predetermined target characteristics, which if necessary can be asingle target characteristic, can be system-oriented characteristicscalculated during the construction of the retarder system or determinedby trial, in particular so-called “worst-case” characteristics, that is,characteristics which are created upon assumption of the occurrence ofpossible unfavorable states in the system. Additionally, variable statedata of the system or the environment, such as for example the ambienttemperature, the vehicle mass, the axle load etc. can be considered inthe characteristics. Alternatively or in addition, for each vehicle orfor each retarder an “adaptive” characteristic can be “programmed” atthe beginning of the operating time, that is, this characteristic is setbased on operating data detected at the beginning of the vehicleoperating time.

By means of the comparison of the actual progression, that is thetemporal progression of the determined actuating pressure, with thetarget progression it is possible to detect critical changes, that is,unusual modifications of the ventilation behavior of the actuatingpressure, in particular in the case of the largely complete draining ofthe retarder or the draining of the retarder to a predetermined fillingcapacity and to initiate suitable measures. In case for example awarning limit is predetermined, by means of the comparison a decisioncan be made as to whether the retarder system can continue to be used(for example with a warning to the driver of the vehicle that the systemhas to be checked) or whether effective immediately the retarder can nolonger be used and for example will be deactivated by retarder control(in this case, expediently a warning is issued to the operator that theretarder has been put out of operation).

In accordance with an expedient embodiment of the invention thepredetermined target progression comprises two target characteristics,namely a warning characteristic and an immobilization characteristic.Either the detected temporal progression of the actuating pressure isimmediately compared with the two characteristics or first only with thewarning characteristic. With the help of the results of the comparisonof the detected temporal progression of the actuating pressure to thewarning characteristic a decision is then made as to whether acomparison with the immobilization characteristic is also necessary. Forexample, in case the retarder torque is to be reduced, that is, if abraking torque reduction is predetermined by the actuating pressurecontrol circuit, after exceeding the warning characteristic a comparisonof the detected actuating pressure to the immobilization characteristicshould expediently take place. If in this case the warningcharacteristic is not exceeded, that is, if the actual progression takesplace so close to the predetermined target progression that no warningis necessary, the comparison with the immobilization characteristic canbe dispensed with.

On the other hand, in case a retarder filling is taking place, that is,if the actuating pressure control circuit predetermines a braking torqueincrease of the retarder, first a comparison is conducted to determinewhether the actual progression falls below the warning characteristic.If this is the case, the detected temporal progression of the actuatingpressure is compared with the immobilization characteristic. In thiscase the last comparison can be eliminated if the warning criterion isnot fulfilled, that is, if the actual progression takes place so closeto the target progression that it does not fall below the warningcharacteristic.

In the case of an exceeding or falling below of the warningcharacteristic—depending on the control case—a warning is expedientlyissued to the operator. In the case of a corresponding exceeding orfalling below of the immobilization characteristic the retarder systemis expediently immobilized, as already described above.

The exceeding or falling below of the target characteristics by theactual progression was presented in the example just described with thehelp of a comparison of the absolute pressure progressions. However, itis also possible to use other variables for error detection or formonitoring the braking torque modification, for example the time betweentwo predetermined points of pressure, which are passed through by theactuating pressure. Another possibility is the comparison of theactuating pressure gradient in one or more predetermined points ofpressure. The advantage of the gradient comparison is the independencefrom the retarder braking torque which is set as the target default ofthe retarder control circuit.

Of course it is also possible to monitor actuating pressure increases,that is, predetermined increases of the retarder braking torque, bymeans of the inventive method. The pneumatic braking pressure is usedexpediently as an additional influencing variable in the predeterminedtarget characteristics, that is, the pressure of the air brake reservoirsystem, for example in or behind an air brake reservoir with workingfluid of the retarder, since this has a direct influence on the increasegradients of the actuating pressure. In vehicles which have the brakingpressure (pV) available as a test signal, this can be included in thecomparison of the actual progression with the target progression. Incase of error, that is, in the case of an increase in pressure outsidethe target characteristic, the possibility should be expediently takeninto consideration that a malfunction of the braking pressure testsignal can also be present.

In vehicles without a braking pressure test signal the minimum possiblebraking pressure (pVmin) as well as the maximum possible brakingpressure (pVmax) are expediently taken into consideration in thecreation of the target progression or the target characteristics. Forexample, in the dynamic comparison of the actual actuating pressure withthe target progression a lower and an upper target characteristic can betaken into consideration, namely a target characteristic which considersthe minimum possible braking pressure and a target characteristic whichconsiders the maximum possible braking pressure. The actuating pressure(actual progression) should then run between these two targetcharacteristics as limiting curves.

The inventive method makes possible the detection of malfunctions bothin the deactivation as well as in the activation of the retarder.Furthermore, the progression during a braking torque modification can bemonitored at a pre-selected target braking torque, whereby the brakingtorque is greater than zero and is less than the maximum braking torqueof the retarder.

Sources of error which can for example lead to pressure gradientsdeviating from the target progression are in particular a disturbance ofthe electro-pneumatic control valve with which the actuating pressure isset, for example by foreign bodies or internal defects, a leakage orcross-sectional changes. A further error cause can lie in a malfunctionof the pressure sensor. Of course, the retarder can also be directlydisturbed by foreign bodies, a leakage or cross-sectional changes, aswell there being errors in the control unit or in the braking pressuresystem.

The invention will be explained in greater detail with the help of theattached figures.

The figures show the following:

FIG. 1 shows a schematic representation of an actuating pressure controlcircuit in whose control unit (electronic control unit) the inventivemethod can be implemented;

FIG. 2 shows an example of a detected actual progression and the targetcharacteristics of the target progression when the retarder isdeactivated;

FIG. 3 shows an example of two target characteristics when the retarderis being activated.

In FIGS. 2 and 3 the actuating pressure P_(Y) is plotted in its temporalprogression, that is, over the time t. In each case, two targetcharacteristics are represented by dashed lines and the actualprogression is represented by a solid line. In addition FIG. 2 shows theactuating pressure gradients P_(Y1) at the time t₁ and P_(Y2) at timet₂.

In FIG. 2 the actuating pressure runs first on a linear high level, thatis, the retarder brakes with a correspondingly great braking torque. Assoon as the operator, by means of activating a corresponding inputdevice, has selected the function that the retarder is to bedeactivated, the actuating pressure P_(Y) begins dropping starting withtime t_(AUSSIGNAL). As one can see, in the represented example thedeactivation process runs in the uncritical region, that is below thewarning characteristic and the immobilization characteristic arrangedabove it.

FIG. 3 shows the activation process, beginning at the time of thet_(EINSIGNAL) activation signal. Here too the activation process runs inthe uncritical region, that is between a predetermined first (minimum)target characteristic based on a minimum possible pressure in an airbrake reservoir for the working fluid of the retarder and a second(maximum) target characteristic based on a maximum possible pressure inthe air brake reservoir.

1. Method for monitoring a braking torque modification of a retarder, inparticular of a motor vehicle, said braking torque modification beingcontrolled by an actuating pressure control circuit comprising apressure sensor that is connected in said circuit. The method comprisesthe following steps: the actuating pressure of the retarder isdynamically detected by means of the pressure sensor that is mounted inthe actuating pressure control circuit; the temporal progression of thedetected actuating pressure is compared with at least one predeterminedtarget progression; a warning is issued and/or a future activation ofthe retarder by a user, in particular the driver of the vehicle, isprevented, based on the actual-target comparison and if predeterminedcriteria have been fulfilled.
 2. Method in accordance with claim 1,characterized by the fact that the predetermined target progression isstored in the form of at least one target characteristic, in particularin a retarder control unit.
 3. Method in accordance with claim 1,characterized by the fact that the comparison is performed by theretarder control unit.
 4. Method in accordance with claim 2,characterized by the fact that the predetermined target progressioncomprises two target characteristics, an advance warning characteristicand an immobilization characteristic, whereby the temporal progressionof the detected actuating pressure is compared with both characteristicsor is first compared with the warning characteristic and in the case ofa braking torque decrease predetermined by the actuating pressurecontrol circuit upon the exceeding of the warning characteristic and inthe case of a braking torque increase predetermined by the actuatingpressure control circuit upon the falling below of the warningcharacteristic is then compared with the immobilization characteristic,and upon the exceeding of the warning characteristic of thepredetermined braking torque decrease and up the falling below of thewarning characteristic in the case of the predetermined braking torqueincrease a warning is issued; and upon the exceeding of theimmobilization characteristic in the case of the predetermined brakingtorque decrease and upon the falling below of the immobilizationcharacteristic in the case of the predetermined braking torque increasea future activation of the retarder by a user, in particular the driverof the vehicle, is prevented.
 5. Method in accordance with claim 2,characterized by the fact that the target characteristic, of which thereis at least one, is stored based on specific design data of theindividual motor vehicle system and variable, detected state data of themotor vehicle system and/or the environment.
 6. Method in accordancewith claim 2, characterized by the fact that the target characteristic,of which there is at least one, is stored as an adaptive characteristicbased on the operating data detected at the beginning of the vehicleoperating time.
 7. Method in accordance with claim 2, characterized bythe fact that the comparison comprises the comparing of the timesbetween two predetermined actuating pressure points of the detectedtemporal progression of the actuating pressure and of the predeterminedtarget characteristic, of which there is at least one.
 8. Method inaccordance with claim 2, characterized by the fact that the comparisoncomprises the comparing of the actuating pressure gradients atpredetermined actuating pressure points of the detected temporalprogression and of the predetermined target characteristic, of whichthere is at least one.
 9. Method in accordance with claim 2,characterized by the fact that at least a first target characteristic ofthe minimum actuating pressure and a second target characteristic of themaximum actuating pressure are stored.
 10. Method in accordance withclaim 9, characterized by the fact that a braking torque increase of aretarder is monitored, and the first target characteristic is createdbased on a minimum possible pressure in an air brake reservoir forworking fluid of the retarder, and the second target characteristic iscreated based on a maximum possible pressure in the air brake reservoir.11. Method in accordance with claim 1, characterized by the fact that adeactivation process of the retarder is monitored.
 12. Method inaccordance with claim 1, characterized by the fact that a braking torquereduction of the retarder is monitored at a predetermined brakingtorque.
 13. Use of a pressure sensor installed in an actuating pressurecontrol circuit of a retarder for the dynamic monitoring of theactuating pressure and for error detection.
 14. Method in accordancewith claim 2, characterized by the fact that the comparison is performedby the retarder control unit.
 15. Method in accordance with claim 3,characterized by the fact that the predetermined target progressioncomprises two target characteristics, an advance warning characteristicand an immobilization characteristic, whereby the temporal progressionof the detected actuating pressure is compared with both characteristicsor is first compared with the warning characteristic and in the case ofa braking torque decrease predetermined by the actuating pressurecontrol circuit upon the exceeding of the warning characteristic and inthe case of a braking torque increase predetermined by the actuatingpressure control circuit upon the falling below of the warningcharacteristic is then compared with the immobilization characteristic,and upon the exceeding of the warning characteristic of thepredetermined braking torque decrease and up the falling below of thewarning characteristic in the case of the predetermined braking torqueincrease a warning is issued; and upon the exceeding of theimmobilization characteristic in the case of the predetermined brakingtorque decrease and upon the falling below of the immobilizationcharacteristic in the case of the predetermined braking torque increasea future activation of the retarder by a user, in particular the driverof the vehicle, is prevented.
 16. Method in accordance with claim 3,characterized by the fact that the target characteristic, of which thereis at least one, is stored based on specific design data of theindividual motor vehicle system and variable, detected state data of themotor vehicle system and/or the environment.
 17. Method in accordancewith claim 4, characterized by the fact that the target characteristic,of which there is at least one, is stored based on specific design dataof the individual motor vehicle system and variable, detected state dataof the motor vehicle system and/or the environment.
 18. Method inaccordance with claim 3, characterized by the fact that the targetcharacteristic, of which there is at least one, is stored as an adaptivecharacteristic based on the operating data detected at the beginning ofthe vehicle operating time.
 19. Method in accordance with claim 4,characterized by the fact that the target characteristic, of which thereis at least one, is stored as an adaptive characteristic based on theoperating data detected at the beginning of the vehicle operating time.20. Method in accordance with claim 5, characterized by the fact thatthe target characteristic, of which there is at least one, is stored asan adaptive characteristic based on the operating data detected at thebeginning of the operating time.